I had that happen on my Tiger Trainer .40 (RIP). It will fly fine without the caps on the tail, but if you really don't like the way it looks, try to cover it with white monokote or make a cap from a coke bottle and cover it with monokote.

Make top and bottom flat pieces using the other cap as a pattern, remember it's reversed. Use a 1/4" strip of plastic cut from a 2L coke bottle to join the two pieces together. (Use hinge tape on the INSIDE of the cap to keep the pieces together). Put it on and cover with monokote. I did this and it only looked OK after about 2 hrs of work. A week later I found my old cap in my truck.